Use vtm output for OpenFOAM to VTK translation

The current foamToVTK and vtkWrite (function object) write legacy files on a per-processor basis. This should be adjusted to use the vtm (multi-block) format that incorporates a vtu file for the internal mesh and vtp files for the boundary patches. The realization might entail collection on the master, or aggregates. The output shall contain all relevant fields within each timestep file.